The present invention relates to an image processing apparatus and method.
In many image processing applications, it is necessary to identify edges in an image, for example to enhance the edges to give them a better visual appearance, to segment an image, or to identify corner points which lie at the intersection of edges in the image.
Known edge detection techniques, for example as described in xe2x80x9cComputer Graphics Principles and Practicexe2x80x9d by Foley, van Dam, Feiner and Hughes, Second Edition, Addison-Wesley Publishing Company ISBN 0-201-12110-7, detect edges by identifying sharp changes in intensity in the image. Such techniques do not provide reliable results in many circumstances, however, particularly when used on images in which an edge has become broken, for example due to lighting, shadows or poor image quality.
One particular application in which edge detection may be used is the creation of three-dimensional computer models of a real-life object using at least two images of the object taken from different positions to determine the relative position of points on the object in two-dimensions and the relative xe2x80x9cdepthxe2x80x9d of the points. To create such models, it is necessary to know the location in each image of points which represent the same actual point on the object. Such points can be determined by identifying corner points in each image and matching corner points from one image with the corner points in another image.
To enable matching points to be easily identified in the images, a number of known systems apply a grid pattern to the object before the images are taken so that the grid lines can be identified in the images and their points of intersection determined. Such a system is disclosed in WO-A-90/10194. Before grid lines can be automatically identified by the image processing system, however, WO-A-90/10194 discloses that it is necessary for a user to xe2x80x9cpatchxe2x80x9d the lines to ensure that they are unbroken. This is particularly time consuming.
The present invention has been made with the above problems in mind, and aims to provide an apparatus and method for detecting edges in an image.
The present invention provides an image processing apparatus or method in which edges in an image are detected on the basis of edge orientation. Edge intensity may optionally be used, as well.
Of course, use of edge detection is not limited to the above applications and many other image processing applications exist where edge detection is used.
In many image processing applications, it is necessary to sub-divide or segment an image. Such applications include object recognition and image compression.
The present invention provides an image processing apparatus or method in which an image is segmented in dependence upon edge strengths in the image.
The present invention provides an image processing apparatus or method in which an image is divided into pieces by connecting points in dependence upon the strength of edges therebetween. The pieces may be non-overlapping.
In many image processing applications, it is necessary to process edges identified in an image to determine whether any of the edges cross, and to remove the cross-overs. Such applications include image segmentation, object recognition and image data compression.
The present invention provides an image processing apparatus or method in which signals defining edges and the strengths thereof are processed to remove crossovers between the edges by considering pairs of edges in decreasing strength order. If two edges are thought to cross, the edge with the lower strength is deleted.